welcome! [railroads.dot.gov]...lt operator training 16 leak testing technique must be of proper...

WELCOME!

Topic Lecturer: Christopher J. Gamblin Director, Technical Services ASNT LEVEL III No. 176360 1

Discussion Scope

LT Method and BLT Technique application for those employees

that are not needing certification to a code and standard.

2

(d) Examination before shipping. (1) No person may offer for transportation a tank car containing a hazardous material or a residue of a hazardous material unless that person determines that the tank car is in proper condition and safe for transportation. As a minimum, each person offering a tank car for transportation must perform an external visual inspection that includes: …

CFR 173.31 (d)

3

Divided into three main categories by American Society of Non-Destructive Testing. Leak Detection, Leak Location, Leak Measurement

Bubble Leak Testing is an example of both Leak Detection, and Leak Location.

Leak Testing Methods

4

Three common LT techniques for tank car inspection: Bubble leak testing – liquid film (BLT) Chemical Reactivity (CRLT) Pressure change or Pressure Decay

Three Techniques of LT

5

LT is a form of NDT that uses either a pressurized or evacuated system to detect the location of leak and possibly measure the leakage through the leak.

LT when compared to other methods, either surface (MT, PT) or Volumetric (UT, RT), has a higher degree of sensitivity to locate the leak or measure leakage.

Leak Testing

6

Leak; Physical hole that exists and not the quantity of fluid

passing through.

Leakage: The flow of fluid through a leak without regard to

physical size of the hole through which flow occurs.

Leak Testing Definitions

Source: ASNT NDT Handbook, 3rd Edition. Volume 1; Leak Testing

Term leak tight is relative. Nothing is truly leak tight and different terms should be used. Terms no detectable leakage, no leakage, or zero leakage truly represent the desired condition before shipping a tank car. Everything leaks, absolute tightness is only theoretical in practice. Nothing made by humans can truly be absolute leak tight.

Leak Tight

8

Leak Path

9

LT techniques are measured in leak rates. The smaller the leak rate detected, the higher the sensitivity. Examples of minimum detectable leak rates:

Leak Rates/Sensitivity

10

Ultrasonic Leak Detector 10-1 std cm3 per second

Bubble Leak 10-3 std cm3 per second

Mass Spectrometer detector probe

10-5 std cm3 per second

Radioactive Isotope 10-8 std cm3 per second


Quantity (mass) of a gas leaking in one second. Volume equal to three dimes stacked vertically.

1 std cm3 per second

11

10-2 10 seconds

10-3 100 seconds

10-5 3 hours

10-8 1 year

10-12 3000 years


(Economic) To prevent material loss that interferes with system operation. (Safety) Prevent fire, explosion, and environmental contamination. (Reliability) Detect unreliable components, and those with leakage rates that exceed standards.

Reasons for Leak Testing

12

LT is an important process to the measure the reliability of the system under test. LT can show a fundamental fault of the system. High leakage rates in specific areas may determine: Gasket improperly aligned Valve connections misaligned or improperly threaded

System Reliability

13

LT is not a direct measurement of continuing system reliability, only a measurement of the reliability at the time of testing. Primary use of LT for railroad tank car industry is to detect installation errors.

System Reliability

14

LT sensitivity depends heavily on the skill level and alertness of the LT operator. LT operators must be trained in the fundamentals of LT to ensure they are performing a LT correctly each time. Common errors: Operators do not look at test joint for an acceptable

period of time not identify all possible leak paths

LT Operator Training

15

Training plans for LT operator personnel should include: Disadvantages and advantages of LT methods Identify hazards with LT Enhancing testing environments Techniques for improving inspection skills Factors affecting LT measurement accuracy Proper ways to carry out and conduct LT methods

LT Operator Training

16

Leak Testing technique must be of proper sensitivity for scope of test, and also be economical value for the technique to be desirable for application. Bubble Leak testing accomplishes both of these criteria, and represents most of the LT performed in the RR Tank Car Tank industry.

Bubble Leak Testing

17

Three techniques classified by the how the liquid used for detection is applied: Liquid Immersion Liquid Film Foam application

Bubble Leak Testing

18 Source: ASNT NDT Handbook, 3rd Edition. Volume 1; Leak Testing

Simple to use, rapid application, and inexpensive Sensitivity is acceptable for use with tank car tanks Enables the observer to locate the exit point of leaks very accurately (compared to Pressure Change Test) Very large leaks and small leaks can be detected, offers a wide range of detection unlike some other techniques.

BLT Advantages

19

BLT allows observer to distinguish real leaks from “virtual” leaks. “Virtual” Leaks are those in which trapped gases are escaped during a test and are observed. Safe to apply BLT with proper inert gases, and testing liquids, in combustible areas.

BLT Advantages


When performing BLT, or any LT technique beyond its limitations, it renders the test inaccurate and the results dangerously false.

LT

BLT Limitations

21

Certain conditions interfere with BLT, and must be corrected prior to testing. Contamination of test specimen Improper test temperatures Contaminated Leak Test solutions Prior contaminates that clog leaks or leak paths Air dissolved in test liquids, or out gassing from

connections. “Virtual Leaks”

BLT Limitations

22

Importance of cleaning test surface Cleaning a tank car connection prior to performing a LT should include as a guideline: Remove by safe means any sings of rust, grease,

oxide films, or other visible surface contaminants.

BLT Limitations – Surface Cleaning

23

Non-technical applications of LT can cause ordinary soap and water combination to be used. While economical, these testing solutions diminish the sensitivity of the test, possibly causing them to be lower than 101 std cm3 per second. Example: Dishwashing soap and water

Commercial vs “Homemade” BLT Solutions

24

Limitations of Common Soap for BLT Soaps form sticky, gummy deposits that can clog

leaks. “Bath tub ring” Soaps are alkaline; pH values of 10.5 to 11.5. Can

cause severe corrosion to Aluminum Alloys. Soaps contain chlorides and borates. These can

cause stress corrosion cracking on stainless steels or titanium alloys. Many valves are SS or 22Ti.



Commercial BLT solutions are favorable over “soap and water” when compared: Have pH between 6-8 Do not form deposits when mixed with “hard water” Viscosity allows low surface tension, allows BLT

solution to spread over surface Stabilized solutions are resistant to bacteria and

maintain sensitivity over long periods of time Allow BLT solution to dry to a clean state Temperature range -30°F to over 150°F




27


28


29

First and foremost, safety is key in working with loaded tank cars or any pressurized vessel. Along with tank car shipping location safety standards, LT safety briefings should include these topics: Working with pressurized vessels Hazards with going on top of, or below tank car.

Process Steps for BLT

30

Clean areas of interest to BLT. Remove dirt, slag, rust, or any foreign debris. Consideration of the cleaning chemical must be taken in consideration for compatibility with BLT solution.


31

Create pressure differential. Creating a high pressure side, and lower pressure side will start leakage to flow. General guidelines state that a minimum of 15 psig (210 kpa) be used as a starting pressure.



Temperature should be checked prior to applying the BLT solution. Use IR or contact thermometers. Must be between temp limits of BLT solution.


33

Apply BLT solution. Flow solution over test area, not creating bubbles in

the process Do not brush or spray unless LT solution is designed

for such application! Gently flowing solution over area will allow complete

coverage. Care should be taken to observe the solution as it is applied.


34

Allow BLT solution to Dwell on the test area for a specific amount of time. Usual Dwell times are 5min -10min

After Dwell time has elapsed, inspect area for bubble formation


35

Inspection should be done in a adequate environment to get the best results for the test. Improve the environment to increase the sensitivity of the test: Increase lighting Better position to keep view angle at 0°-15° If possible, improve temperature, wind, humidity Use BLT solutions that have higher visibility


36

Test joint must show no bubble formation to be considered to pass the leak test BLT will show bubbles collapsing and reforming to indicate a leak

Inspection

37

LT procedure should be written by an ASNT Level III Allows for uniform application by all LT operators Specifies the minimum requirements for conducting a test A procedure should list all aspects of the LT that are essential to be met Can provide reasonable certainty that a specific sensitivity is being met

LT Procedure

38

Procedures should include: Cleaning requirements LT solution Temperature limits Test Pressure Acceptable leak rates (Acceptance Criteria) Reporting of a leak Cleaning practice

LT Procedures


CONTACT INFO Christopher Gamblin:

Watco Compliance Services, LLC EMAIL: [email protected] PHONE:713-703-5123

THANK YOU!

40

welcome! [railroads.dot.gov]...lt operator training 16 leak testing technique must be of proper...

Documents